In an environment with multiple compatible VMware products, it is strongly recommended to follow a specific sequence to install and update to the latest patches.
See Knowledge Base article 2037630.

Caution concerning upgrades of vCenter Server 5.1 to 5.1.0 U1 in non-English environments. You must install Single Sign On (SSO) through the command line.
See Knowledge Base article 2037976.

Update vSA after upgrading to vCenter Server 5.1U1: vSA 5.1.1 customers must upgrade to vSA 5.1.3 after upgrading their vCenter Server to 5.1 Update 1. For more information, see the release notes linked below.
See vSA Release Notes

Login issue after updating to vCenter Server 5.1U1: customers that have large numbers of domain groups may be prevented from logging into vCenter Server 5.1 Update-1 with AD credentials. For more information, see the KB linked below.
See KB 2050941